1. Field of the Invention
The present invention relates to a fixing device for fixing toner on a sheet by heating the toner, and an image forming apparatus including the fixing device.
2. Description of the Related Art
An image forming apparatus of an electrophotography scheme or electrostatic recording scheme includes a fixing device used to fix an unfixed toner image formed on a sheet. According to Japanese Patent Laid-Open No. 06-202513, a fixing device, in which a heat generation layer is provided to a fixing film itself, and which supplies a current to this heat generation layer to directly heat the fixing film so as to heat and fix a toner image, has been proposed. This fixing device has merits of a short time period required from the beginning of power supply until a fixable state is reached, and a small power consumption amount. However, since the fixing device of Japanese Patent Laid-Open No. 06-202513 supplies electric power to the heat generation layer using a brush electrode, it readily causes heat generation unevenness in a circumferential direction of the fixing film. This is caused by wearing of the electrode due to sliding contact and an oxide layer formed upon discharging.
In order to solve this problem, according to Japanese Patent Laid-Open No. 2002-123113, a fixing device that supplies electric power to a heating element in a non-contact manner has been proposed. More specifically, by magnetic coupling between primary and secondary coils, each including a core and coil, electric power is supplied from a power source connected to the primary coil to a heating element connected to the secondary coil.
However, in the fixing device of Japanese Patent Laid-Open No. 2002-123113, since a ferrite core included in a fixing roller rotates together with the fixing roller, the rotation load on the fixing roller becomes heavier. Furthermore, when the fixing roller is made of a flexible film-like member, the ferrite core as a load causes deformation, such as torsion, in the film. When such a problem is to be solved by increasing the rigidity of the film, the heat capacity of the film is increased, resulting in a disadvantageous lengthening of the time period from the beginning of power supply until a fixable state is reached, and an increase in power consumption.